--M [0069] wherein T is a target, M is a marker moiety and L is a chemical group covalently linking the M to T, the chemical group L comprising a backbone that comprises at least one rigid group that comprises one or more of: [0070] (d) multimers of (a), (b) or (c), and (e) any combinations of (a), (b), (c) and (d). [0071] The present invention also provides a labeling reagent comprising R--L--M [